Freon R-134a (1,1,1,2-tetrafluoroethane) called a new refrigerant is now mainly used in refrigerators, etc., but it is expected that its use would be prohibited in future in view of problems of environmental control, etc. Hydrocarbon gases and carbon dioxide are now regarded as important substitutes for such a refrigerant. Hydrocarbon gases have a considerably high risk of explosion or combustion and the world trend toward the next generation refrigerant is shifting to carbon dioxide.
Carbon dioxide requires a higher pressure than freon and also has higher permeability and solubility into ordinary polymer materials and thus has a higher chance of blister (foaming) generation. Even if there is no blister generation, carbon dioxide gas permeates through the polymer materials, resulting in failure of pressure maintenance or tight sealing.
Even rubber materials have a high carbon dioxide gas permeability in general, and the permeability is considerably high particularly under pressure of 10 atm or higher, resulting in failure of tight sealing of carbon dioxide gas. Furthermore, carbon dioxide is very soluble into polymers, giving rise to considerable polymer swelling. Thus, no rubber material parts have been actually applied to apparatuses using carbon dioxide.
In case of the conventional freon gas refrigerants, hydrogenated NBR, EPDM, etc. have been used as molding materials for sealing materials, but these rubber materials considerably swell or blister through contact with carbon dioxide as disadvantages.